Aqueous polymer dispersions are widely used for providing protective polymer coatings in a variety of different applications. Examples include latex paints, watererproofing emulsions for roofs, foundations and other building structural members, caulks and other sealants. Typically, the polymers used to make such aqueous polymer dispersions have low glass transition temperatures, since this helps make the protective coating formed tough and coherent.
In accordance with this invention, the mechanical properties of protective polymer coatings made from an aqueous polymer dispersion, especially those made from a polymer having a lower glass transition temperature, are improved by including in the dispersion solvent softened nanoparticles which are made from a polymer having a higher glass transition temperature.
Thus, this invention provides an aqueous polymer dispersion comprising an aqueous dispersion of primary polymer particles formed from a polymer having a lower glass transition temperature, the aqueous dispersion further containing solvent softened polymer nanoparticles formed from a polymer having a higher glass transition temperature, the higher glass transition temperature being at least 10° C. higher than the lower glass transition temperature.
In addition, this invention also provides a process for improving the mechanical properties of a polymer protective coating formed from a primary aqueous dispersion of a polymer having a lower glass transition temperature, the process comprising including in the primary aqueous dispersion solvent softened polymer nanoparticles formed from a polymer having a higher glass transition temperature at least 10° C. higher than the lower glass transition temperature in an amount sufficient to improve the mechanical propertied of the protective coating.
In addition, this invention also provides improved polymer protective coatings which are made by depositing the above improved aqueous polymer dispersions on a substrate and allowing the deposited aqueous polymer dispersions to dry.